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Are all of the numbers in a certain list of 15 numbers equal?

1. The sum of all the numbers in the list is 60 2. The sum of any 3 numbers in the list is 12

Guys, can you tell me what is the logic disguided in the second stat.? Thanks!

There are a few ways to look at this. One is to reverse the problem: say they aren't all equal. Write the set in increasing order: {a, b, c, ..., m, n, o}, and while some of these might be equal, we must have a < o. Well clearly then the sum of the three smallest numbers is less than the sum of the three largest, (a+b+c < m+n+o), so the sum of any three numbers in the list isn't always the same. So the only way S2 can be true is if all the numbers are equal.
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Re: Equal number DS-find the shortcut [#permalink]

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18 Jul 2009, 18:29

IanStewart wrote:

sondenso wrote:

Are all of the numbers in a certain list of 15 numbers equal?

1. The sum of all the numbers in the list is 60 2. The sum of any 3 numbers in the list is 12

Guys, can you tell me what is the logic disguided in the second stat.? Thanks!

There are a few ways to look at this. One is to reverse the problem: say they aren't all equal. Write the set in increasing order: {a, b, c, ..., m, n, o}, and while some of these might be equal, we must have a < o. Well clearly then the sum of the three smallest numbers is less than the sum of the three largest, (a+b+c < m+n+o), so the sum of any three numbers in the list isn't always the same. So the only way S2 can be true is if all the numbers are equal.

Re: Are all of the numbers in a certain list of 15 numbers [#permalink]

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26 Nov 2009, 19:09

1

This post received KUDOS

B Let's say the list includes a,b,c,d... According to B, a+b+c = b+c+d = 12 => a=d. Similarly, all numbers in the list are equal. Hence B.
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Re: Are all of the numbers in a certain list of 15 numbers [#permalink]

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27 Nov 2009, 21:28

let analyze satement 2

the sum of any 3 numbers is 12.

let assume 15 numbers are a,b,c,d,e,f,g,h,i,j,k,l,m,n,o

For example a+b+c= 4+4+4=12,d+e+f=4+4+4=12,if we assume like this then statement b is sufficient

but what can i do if a+b+c= 4+4+4=12,d+e+f=4+3+5=12,g+h+i=1+6+5=12......from this example all numbers couldnt be equal so b is not sufficient .plz expain

Re: Are all of the numbers in a certain list of 15 numbers [#permalink]

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27 Nov 2009, 21:33

TomB wrote:

let analyze satement 2

the sum of any 3 numbers is 12.

let assume 15 numbers are a,b,c,d,e,f,g,h,i,j,k,l,m,n,o

For example a+b+c= 4+4+4=12,d+e+f=4+4+4=12,if we assume like this then statement b is sufficient

but what can i do if a+b+c= 4+4+4=12,d+e+f=4+3+5=12,g+h+i=1+6+5=12......from this example all numbers couldnt be equal so b is not sufficient .plz expain

if we take f,h,i from ur list the sum is not 12, from S2, any 3 numbers should total 12... so they all have to be 4
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Re: Are all of the numbers in a certain list of 15 numbers [#permalink]

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28 Nov 2009, 23:04

JimmyWorld wrote:

Are all the numbers in a certain list of 15 numbers equal?

1) The sum of all the numbers in the list of 60. 2) The sum of any 3 numbers in the list is 12.

Not sure on 2). Wonder if someone could explain? Thank you

Look for the clue: sum of "any three number" is 12.

Sum of any 3 numbers from a, b, c, d, e, f, g, h, i, j must be 12. That is possible only if all these numbers must be equall and integers i.e. 4.

TomB wrote:

let analyze satement 2

the sum of any 3 numbers is 12.

let assume 15 numbers are a,b,c,d,e,f,g,h,i,j,k,l,m,n,o

For example a+b+c= 4+4+4=12,d+e+f=4+4+4=12,if we assume like this then statement b is sufficient

but what can i do if a+b+c= 4+4+4=12,d+e+f=4+3+5=12,g+h+i=1+6+5=12......from this example all numbers couldnt be equal so b is not sufficient .plz expain

Are all of the numbers in a certain list of 15 numbers equal? (1) The sum of all the numbers in the list is 60. (2) The sum of any 3 numbers in the list is 12.

I think I've posted different solutions to this question elsewhere, but one way to look at Statement 2:

let a, b, c and d be four random numbers from the list. From Statement 2, since the sum of *any* three numbers is 12, we know

a + b + c = 12 d + b + c = 12

and if you subtract the second equation from the first, you find that a - d = 0, so a = d. Since a and d are just randomly chosen numbers from the list, we could do the same thing for any of the numbers in our list, and so they all need to be equal. Since Statement 1 is not sufficient, the answer is B.
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Re: Are all of the numbers in a certain list of 15 numbers equal? [#permalink]

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03 Aug 2010, 15:42

This was my approach

You have 15 numbers that add up to 60. Factoring 60 you get that the only combination of two factors that have 15 must have 4 on them. There is no other number than 4 that repeated 15 times add up to 60

1) You know that you need a 4 for the statement to be sufficient, but as it can be any other number or fraction is not sufficient.

2) Any combination of 3 numbers of the list add 12. You can see that 4 is your lucky number, therefore answer is B.

Re: Are all of the numbers in a certain list of 15 numbers equal? [#permalink]

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04 Aug 2010, 20:09

IanStewart wrote:

zest4mba wrote:

Are all of the numbers in a certain list of 15 numbers equal? (1) The sum of all the numbers in the list is 60. (2) The sum of any 3 numbers in the list is 12.

I think I've posted different solutions to this question elsewhere, but one way to look at Statement 2:

let a, b, c and d be four random numbers from the list. From Statement 2, since the sum of *any* three numbers is 12, we know

a + b + c = 12 d + b + c = 12

and if you subtract the second equation from the first, you find that a - d = 0, so a = d. Since a and d are just randomly chosen numbers from the list, we could do the same thing for any of the numbers in our list, and so they all need to be equal. Since Statement 1 is not sufficient, the answer is B.

I still didn't get you....

There are 15 different numbers, but we took only 4 for our example.

what if a + b+ c = 12 and d + e+ f = 12
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GGG (Gym / GMAT / Girl) -- Be Serious

Its your duty to post OA afterwards; some one must be waiting for that...

Are all of the numbers in a certain list of 15 numbers equal? (1) The sum of all the numbers in the list is 60. (2) The sum of any 3 numbers in the list is 12.

I think I've posted different solutions to this question elsewhere, but one way to look at Statement 2:

let a, b, c and d be four random numbers from the list. From Statement 2, since the sum of *any* three numbers is 12, we know

a + b + c = 12 d + b + c = 12

and if you subtract the second equation from the first, you find that a - d = 0, so a = d. Since a and d are just randomly chosen numbers from the list, we could do the same thing for any of the numbers in our list, and so they all need to be equal. Since Statement 1 is not sufficient, the answer is B.

I still didn't get you....

There are 15 different numbers, but we took only 4 for our example.

what if a + b+ c = 12 and d + e+ f = 12

Say our list is:

a, b, c, d, e, f, g, h, i, j, k, l, m, n, o

I just took the first four numbers and proved a=d. There's nothing special about the first four numbers in the list; I can use the same logic to prove that any two numbers are equal here. For example, if I want to prove that b=d, we have

b + c + a = 12 d + c + a = 12

Subtract the second equation from the first:

b - d = 0 b = d

So now we know that b = d. Since we saw that a=d as well, a, b and d are all equal. We can do this for all the letters in the list, so they all must be equal.
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Re: Are all of the numbers in a certain list of 15 numbers equal? [#permalink]

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05 Aug 2010, 10:23

Question type : yes/no

Given to us that a list contains 15 numbers

statement 1) sum of all numbers is 15.

The statement does not answer the question whether the all numbers are the same as all numbers can be zero except one which might be 60.

INSUFFICIENT

statement 2) The sum of any 3 numbers in the list is 12.

so this basically mean x1+x2+x10 = 12 x3+x4+x15 = 12 ... so on

so for the sum to be twelve for any numbers in the List, the numbers must be 4 each. This answers our original question of if all the numbers are equal or not. SUFFICIENT

Re: Are all of the numbers in a certain list of 15 numbers equal? [#permalink]

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07 Aug 2010, 01:07

zest4mba wrote:

Are all of the numbers in a certain list of 15 numbers equal? (1) The sum of all the numbers in the list is 60. (2) The sum of any 3 numbers in the list is 12.

Re: Number properties from OG 12 DS133 [#permalink]

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23 Sep 2010, 00:49

Argh, this happens to me about 1/2 the time I come here to post about an explanation. While I'm typing, or right after I post the light bulb comes on over my head.

I was misinterpreting statement 2. I was thinking the sum of each consecutive group of 3 numbers equals 12. Obviously if any 3 numbers sum to equal twelve, each number must be 4. Therefore, all numbers in the list are equal.